Input Catalogs

Dr. Rosa sent me two catalogs from his previous work on Tycho's papers. The first catalog contained 788 stars, that he had selected from the larger final catalog of Tycho (approximately 1000 stars). The stars left out were the ones with poorer accuracy, as noticed by others.

That catalog, including modern positions from the Yale Bright Star Catalog, can be found here. That catalog also lists the short-forms that I used for all the star names. The short form is usually the Greek letter (in lower case) with the three letter constellation name (first letter capitalized) appended. If the Greek letter was not used, then the star number in the constellation was used. Examples: Sirius-> alphaCMa, Rigel-> betaOri, 19 Draconis-> 19Dra.

He also sent a shorter list, here, of 100 stars that were Tycho's primary stars - those that Tycho had most carefully measured.

I needed these baseline catalogs so that I could measure the same stars that Tycho had measured.

I took these two catalogs, converted the ra/dec to decimal degrees, and precessed them to a nearby year, 2020. This was necessary because some stars had shifted by many hundreds of arcsec over the 20 years due to the precession of the Earth's axis during that span. I did not correct for proper motion. I converted all working catalogs to decimal degrees, and also used decimal degrees in all my software and data files. Hours/degrees-minutes-seconds are painful to deal with.

During these manipulations, I went back and forth between .xls files and .csv files, as convenience dictated. I later regretted this for the following reason. When a spreadsheet program contains decimal numerical data, it saves numbers with 6+ digit accuracy (real variables) or 13+ digits (double precision variables) in its default file structure. If a file containing numerical data is saved in comma-separated-variable format (.csv), the saved file has the numbers saved as text. Had I displayed, say, dec to only two decimal places in the original spreadsheet, and then saved it as a .csv file, then the accuracy would only be a few digits instead of the expected 6+ digits. If the .csv file was then read back in, and later saved it in the default format, then the original accuracy would have been permanently lost. (Although I give this explanation, using the Excel formats as an example, Mac 'Numbers', Kaleidagraph, or any other spreadsheet program will have the same behavior.) I personally use the program 'Kaleidagraph', rather than Excel, because I prefer its graphing capabilities.

The reason I came to regret my earlier cavalier attitude about file formats came when I realized I was going to have to rely heavily on sorting to develop my planning and analysis processes. I had been consistent with retaining star names, but I had not been consistent with the exact numerical entries (ra/dec, etc.). I did not want to sort by star name because that doesn't produce an ordering on the sky. The ability to sort using right ascension was desired, because it naturally leads to the progression of the stars during the night, and during the year.

But I had already started observing using several versions of the 100 star catalog. They now all had slightly different right ascension(ra) values, and they had been stored on several computers, including the scope computer itself. I found that when I sorted the data, stars that had similar ras often interleaved with each other, which made the extraction of observations on individual stars much more difficult. I finally had to go in and hand-edit both my primary star catalog (100 entries) and then my full catalog (788 entries) to make sure that the ra values would not interleave, and then redistribute these working catalogs onto my computers. Chaning the ra values by as much as +/-0.005 degrees ensured that the all the ras were different and consistent. (0.005 degrees = 18 arcsec, and my encoder resolution was 0.009 deg = 34 arcsec.) If you download my starter catalogs, mentioned above, you will see that all the ras are rounded to the nearest 0.01 degrees.

I use the terms 'primary star' and 'secondary star' a bit loosely. Primaries are the 100 or so bright stars used to form the backbone of the catalog. They get observed more heavily than the 'secondary stars', the remaining 600+ stars. But, when I built my working catalogs, I realized that I wanted the 'secondary' catalogs to also include the primary stars because I needed them to produce all the star pairs for the separation measurements. To that end, the 'primary' stars are included in the 'secondary' catalogs, but the star names of the primaries have a tilde (~) appended to them. i.e. alphaLyr~, so that I could later distinguish them from the secondary stars.

After these modifications, I had my working primary catalog (here) and master catalog (here).

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